1. Field of the Invention
The present invention relates to a gas compressor and more particularly to a gas compressor which allows electricity generation by recovering exhaust heat from the gas compressor.
2. Description of the Related Art
It is said that the energy consumed by gas compressors such as air compressors and the like corresponds to about 20 to 25% of the energy consumed in the entire factory. Therefore, if it is allowed to recover exhaust heat from the gas compressors, the effect thereof will be increased. In particular, it has a large effect to recover and use the exhaust heat from the gas compressors in order to attain the goal of reducing carbon dioxide emissions arising from the problem of global warming simultaneously.
The gas compressor includes a compressor body for compressing a gas such as air or the like, a motor for driving the compressor body, a cooling system for cooling heat generated by compression in the compressor body and the like. In addition, in the gas compressor, assuming that power (electrical power) which is into the motor is 100%, a heat rate (exhaust heat rate) cooled by the cooling system corresponds to 90% or more of the input power and the exhaust heat is normally emitted into the atmosphere. This means that considerably much energy (the heat rate) is exhausted to the atmosphere. Although high efficiency of the compressor body and the motor is being promoted in order to reduce the exhaust heat rate, the effect thereof is limited to several percent and therefore effective utilization of the exhaust heat from the gas compressor is sought for.
Although, as for effective utilization of the exhaust heat from the gas compressor, examples such as utilization thereof for heating a room, effective use thereof for heating water, effective use thereof for preheating water supplied to a boiler and others are given, it is expected that practical use of the exhaust heat for generating electricity by effectively using the Rankine cycle that a low-temperature evaporating medium is used will be accelerated.
Incidentally, as related art of this kind, there is proposed a technology as described in Japanese Patent Application Laid-Open No. 2011-12659. The technology described in Japanese Patent Application Laid-Open No. 2011-12659 is the one that heat is exchanged between compressed air discharged from a compressor body and a working fluid in the Rankine cycle and the Rankine cycle is established by driving an expander with the vaporized working fluid, thereby generating electricity.
The technology described in Japanese Patent Application Laid-Open No. 2011-12659 is the one that the working fluid of the Rankine cycle is heated with compressed gas which has been compressed by the compressor body and has reached a high temperature and the expander is driven with the vaporized working fluid to generate electricity. That is, it allows effective utilization of the exhaust heat which has been discarded to the atmosphere so far. However, when it is thought to utilize the generated power as a power supply for driving an auxiliary machine such as a cooling fan or the like in a compressor unit which configures the gas compressor, an electricity generation amount (an amount of generated electricity) which is sufficient to drive the auxiliary machine such as the cooling fan or the like is not obtained for a while after start of operation of the gas compressor by the technology described in Japanese Patent Application Laid-Open No. 2011-12659.
In addition, since the exhaust heat rate is varied with a change in amount of the compressed gas generated by the gas compressor still after start of operation of the gas compressor, the electricity generation amount is also varied and a shortage of the electricity generation amount used for driving the auxiliary machine sometimes occurs.
Therefore, it has such a disadvantage that it is difficult to utilize the generated power for driving the auxiliary machine such as the cooling fan or the like in the compressor unit.
Incidentally, although it is also conceivable to store and use the generated power or to return it to a commercial power supply, the cost of equipment for storage is required in order to store the generated power and the cost of installation of a power conditioner is required in order to return it to the commercial power supply.